Referring to FIG. 1, a cross sectional perspective view of a trench metal-oxide-semiconductor field effect transistor (TMOSFET) 100 according to the conventional art is shown. The TMOSFET 100 includes, but is not limited to, a plurality of source regions 110, a plurality of gate regions 115, a plurality of gate insulator regions 120, a plurality of body regions 125, a drift region 130, and a drain region 135.
The drift region 130 is disposed between the drain region 135 and the body regions 125. The source regions 110, gate regions 115 and the gate insulator regions 120 are disposed within the body regions 125. The gate regions 115 and the gate insulator regions 120 may be formed as striped or closed cell structures. The gate insulator region 120 surrounds the gate regions 115. Thus, the gate regions 115 are electrically isolated from the surrounding regions by the gate insulator regions 120. The gate regions 115 are coupled to form a common gate of the device 100. The source regions 110 may be formed along the periphery of the gate insulator regions 120. The source regions 110 are coupled to form a common source of the device 100. The source regions 110 are also coupled to the body regions 125, typically by a source/body contact (not shown).
In one implementation, the source regions 110 and the drain region 135 may be heavily n-doped (N+) semiconductor, such as silicon doped with phosphorous or arsenic. The drift region 130 may be lightly n-doped (N−) semiconductor, such as silicon doped with phosphorous or arsenic. The body regions 125 may be p-doped (P) semiconductor, such as silicon doped with boron. The gate region 115 may be heavily n-doped (N+) semiconductor, such as polysilicon doped with phosphorous. The gate insulator regions 120 may be an insulator, such as silicon dioxide.
When the potential of the gate regions 115, with respect to the source regions 110, is increased above the threshold voltage of the device 100, a conducting channel is induced in the body region 125 along the periphery of the gate insulator regions 120. The TMOSFET 100 will then conduct current between the drain region 135 and the source regions 110. Accordingly, the device is in its ON-state.
When the potential of the gate regions 115 is reduced below the threshold voltage, the channel is no longer induced. As a result, a voltage potential applied between the drain region 135 and the source regions 110 will not cause current to flow there between. Accordingly, the device 100 is in its OFF-state and the junction formed by the body region 125 and the drain region 135 supports the voltage applied across the source and drain.
The lightly n-doped (N−) drift region 130 results in a depletion region that extends into both the body regions 125 and the drain region 130, thereby reducing the punch through effect. Accordingly, the lightly n-doped (N−) drift region 130 acts to increase the breakdown voltage of the TMOSFET 100.
The channel width of the TMOSFET 100 is a function of the length of the plurality of the source regions 110 along the periphery of the gate insulator regions 120. The channel length of the device 100 is a function of the body region 125 between the source regions 110 and the drift region 130 along the periphery of the gate insulator regions 120. Thus, the device 100 provides a large channel width to length ratio. Therefore, the TMOSFET device 100 may advantageously be utilized for power MOSFET applications, such as switching elements in a pulse width modulation (PWM) voltage regulator.